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e-e- E n eV n = 1 ground state n = 3 0 n = ∞ n = n = 4 ionisation N.B. All energies are NEGATIVE. REASON: The maximum energy is the energy to ionise the electron. However an ionised electron feels no attraction to the nucleus so it must have zero potential energy. It follows that energies less than the ionisation energy must be negative

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e-e- E n eV n = 1 ground state n = 3 0 n = ∞ n = n = 4 ionisation If a hydrogen atom has its electron in the lowest energy level (ie -13.6eV) it is said to be in the ground state. If an electron absorbs energy and moves to a higher energy level (ie an excited state) it will be unstable and quickly fall back to the ground state, releasing energy as a photon as it falls. Sometimes the energy of these photons correspond to the energy of visible light.